Canadian authorities are investigating a man from London, Ontario, they say associated with two men from there who died in January, allegedly as part of the team of terrorists who attacked an Algerian gas plant.

Aaron Yoon isn't thought by Canadian authorities to have taken part in the attack, but joined Xristos Katsiroubas and Ali Medlej in Morocco before the assault happened, said people familiar with the matter and with Mr. Yoon....